1. Field of the Invention
The present invention relates to a method and a device for providing cost information for junctions in a road network in a navigation system. The invention especially, but not exclusively, relates to providing cost information for junctions in vehicular navigation and use of that cost information in determining a route.
2. Related Art
Performing route searches on road network in a navigation unit has become increasingly important. Such route searches are typically performed based on map data in a map database that provides information on, inter alia, road segments, their connectivity, and possibly additional information such as the orientation and length of the road segment. Technically, road segments and intersections form a graph on which a route search is performed. To perform a route search, a least-cost search is typically performed on the graph based on a cost model. Different cost models may be employed to find routes that are optimized with regard to different quantities. For example, a cost model that provides information on the travel time associated with the different road segments in the road network may be used for a fastest route search. A cost model that provides information on the fuel consumption associated with the different road segments in the road network may be used for a search for a route having optimum fuel consumption. The cost information associated with the different road segments for the various cost models, such as fastest route, route having least fuel consumption etc., may also be provided in a database.
For various cost models, the costs associated with intersections may significantly affect the result of the route search. For illustration, waiting times at road junctions (or commonly called intersections) in an urban area may significantly add to the total costs in terms of time or fuel consumption that are associated with a route. When information on the costs associated with intersections are set by a human expert, the cost values may not correctly reflect the manifold types of intersections that exist and manoeuvres that may be performed therein. Storing individual cost values for intersections on a per intersection basis may significantly add to storage space requirements.
Accordingly, a need exists for providing cost information associated with junctions (intersections) and for methods of determining a route that utilizes such information. In particular, a need exists for an approach that accounts for the fact that there are many different types of intersections and possible actions performed in the intersections. A need also exists to keep the storage space required for providing the cost information associated with intersections at moderate levels.